Dr. Harvey Feinberg, the president of the Institute of Medicine, once told me that a serious flu pandemic was a bit like an asteroid hitting the Earth—in any given year there was a very low probability cosmic disaster would strike, but if it did, the consequences for the world would be, well, catastrophic. The problem is that human beings and the governments they run aren't very good at preparing for low-probability, high-consequence events.

That might be why it's been so hard for the global health community to raise the necessary funds to really combat avian influenza, and  prepare for the pandemic that will be coming one day.

Today the World Bank reported that an additional $1.2 to $1.5 billion would be needed over the next two to three years to fight avian flu as it spreads through Asia, parts of Europe and perhaps most dangerously, Africa, which will need an additional $466 million alone. This comes on top of $1.9 billion pledged by the international community in Beijing last January.

Much of that funding—assuming it is ever delivered—will be used to compensate poultry farmers whose flocks need to be culled because of infection. Ensuring that farmers are willing to cooperate with anti bird-flu efforts is the best way to slow the spread of the disease among animals—and they only way to do that, is to make sure they get paid.

But is it really worth spending so much to control a disease that, for all the hype, has only killed 154 people since 2003—less than the number who die every three minutes from AIDS? There's a legitimate argument to make that we shouldn't let avian flu crowd out funding in developing countries for more regular killers, like diarrhea or malaria.

But that's where the asteroid analogy comes in handy. If a severe pandemic does strike, the World Bank has warned it could cost the global economy up to $2 trillion, with human damages that would be incalculable. A little insurance might be worth it.

—By Bryan Walsh/Tokyo